This paper reports on an initial investigation of a switched inertance device (‘SID’). Using this device, flow and pressure can be varied by a means that does not rely on dissipation of power. The device can provide a step-up or step-down of pressure or flowrate, analogous to a hydraulic transformer. Simulated and experimental results on a prototype device show a promising performance. The device could potentially provide very significant reduction in power consumption over conventional valve-controlled systems, provided that noise issues and some other practical problems can be overcome.
Tests have been performed on a range of different poppet and disc valves operating under steady flow, non-cavitating conditions, for Reynolds numbers greater than 2500. The working fluid was water, and the axisymmetric valve housing was constructed from clear perspex to facilitate flow visualization. Measured flow coefficients and force characteristics show marked differences depending on valve geometry and opening. These differences are explained with reference to visualized flow patterns.
The difficulties involved in measuring a pump fluid-borne noise rating are discussed. A new test method is described for measuring the source flow ripple and source impedance of positive displacement hydraulic pumps. This is called the ‘secondary source’ method, and is based on the analysis of the wave propagation characteristics in a circuit which includes the pump under test and an additional source of fluid-borne noise.
This paper describes a method of modelling time-varying flow in hydraulic pipelines which may be incorporated into time domain simulations of hydraulic systems operating with variable time steps. A previously reported finite element method is extended. New approximations to frequency-dependent friction for laminar and turbulent flow are presented. These are applicable to this finite element method as well as the method of characteristics and finite difference methods. Simulation results are compared against theory and excellent agreement is found.
Simulations of flow through poppet valves were performed using a proprietary finite volume computational fluid dynamics program. A range of valve geometries was simulated, and the flow was turbulent, incompressible and steady. Simulations were compared with experimental measurements and visualized flow patterns. Qualitative agreement between simulated and visualized flow patterns was good. However, errors in the prediction of jet separation and reattachment resulted in quantitative inaccuracies. These errors were due to the limitations of the upwind differencing scheme employed and the representation of turbulence by the κ-ɛ model, which is known to be inaccurate when applied to recirculating flow.
The performance of hydraulically actuated machine systems could be improved with the use of valves that have high bandwidth and high flowrates under low pressure drops. Although high flowrates can be achieved using very large spool strokes and/or diameters, the overall bandwidth of the valve will be reduced. Research has therefore been undertaken on a prototype valve design incorporating the Horbiger plate principle, which utilizes multiple metering edges to allow high flowrates to be obtained at low pressure drops and small poppet displacements. The valve is directly activated using a piezoelectric actuator to achieve a fast dynamic response. Valve performance is assessed using a mathematical model that includes the piezoelectric actuator and power amplifier, the supply flow, fluid squeeze forces, end stop response, and valve mechanical components. The steady state relationship between valve flow, force and pressure drop, and the fluid inertance, were determined using computational fluid dynamics software. The simulation model has been validated using test data obtained from experimental tests undertaken on a prototype valve. Good agreement is obtained between the predicted and measured results and it is shown that the valve is capable of opening or closing fully in less than 1.5 ms, and can pass a flow of 65l/min at a pressure drop of 20 bar.
An improved method for simulating frequency-dependent friction in laminar pipe flow using the method of characteristics is proposed. It has a higher computational efficiency than previous methods while retaining a high accuracy. By lumping the frequency-dependent friction at the ends of the pipeline, the computational efficiency can be improved further, at the expense of a slight reduction in accuracy. The technique is also applied to the transmission line method and found to give a significant improvement in accuracy over previous methods, while retaining a very high computational efficiency.
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